1997 chevy s10 pickup the abs light will not go out.

Question edited for clarity.
Question moved to model category.

Yes there are three o2 sensors

Bank 1 in the exhaust manifold
Bank 2 in the exhaust manifold
One after the Catalytic Converter.

Not sure what you mean 'where is the best place to put it'? The scan tool tells you which one needs replacing by a P**** Code, or are you just replacing one for fun?

Answered here on JustAnswer dot com

The o2 sensors are located in the exhaust pipe. The one you are looking for is the post cat sensor. The sensor furthest back in the pipe after the catalytic converter.
Mar 19, 2007

Chevy S10 Oxygen Sensor Location: Q&A Guide - JustAnswer

Common causes of the P0420 code

• Damaged muffler or leaks in the muffler.
• Damaged exhaust manifold or leaks in the exhaust manifold.
• Damaged exhaust pipe or exhaust pipe leaks.
• A misfire in the engine.
• Oil contamination in catalytic converter.
• Faulty catalytic converter (most common).
• Faulty engine coolant temperature sensor.
• Faulty front oxygen sensor.
• Faulty rear oxygen sensor.
• Damaged oxygen sensor wiring.
• Oxygen sensor wiring that is not properly connected.
• Damaged oxygen sensor connectors
• A leaking fuel injector.
• High fuel pressure.
• Use of the wrong kind of fuel (using leaded fuel instead of unleaded fuel)

Anrez, your 1991 Chevy trucks O2 sensor could be located in the Y pipe just ahead of converter or in the front portion of the converter.
Check the attached links,instruction and guides, Good luck
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this age vehicle has only one sensor so follow the exhaust pipe down from the manifold and you will find it with no problem

Catalytic Converter Removal & Installation 2.2L Engine To Remove:
Catalytic converter 2.2L engine

1. Raise and safely support the vehicle.
2. Disconnect the heated oxygen sensor (HO2S) electrical connector.
3. Remove the exhaust manifold pipe flange mounting nuts from the catalytic converter.
4. Remove the catalytic converter flange mounting nuts from the muffler.
5. Remove the catalytic converter from the muffler.
6. Remove the catalytic converter from the rear hanger bracket insulator.
7. Remove the catalytic converter.
8. Remove the (HO2S) from the catalytic converter.

To Install:

1. Install the (HO2S) to the catalytic converter.
2. Install a new gasket and the catalytic converter to the muffler.
3. Install catalytic converter to the catalytic converter hanger.
4. Install the catalytic converter flange mounting nuts to the muffler flange.
   • Tighten to 26 ft lbs (35 Nm).
5. Install the catalytic converter flange mounting nuts to the exhaust manifold pipe flange.
   • Tighten to 26 ft lbs (35 Nm).
6. Connect the heated oxygen sensor (HO2S) electrical connector.
7. Lower the vehicle.

------ Catalytic Converter Removal & Installation 4.3L Engine To Remove:

1. Raise and safely support the vehicle.
2. Raise and support the transmission.
3. Remove the transmission support
4. Disconnect the left and right pre-converter heated oxygen sensor (HO2S) electrical connector.
5. Disconnect the post-converter (HO2S) connector. Muffler flange and gasket
   
   
6. Remove the catalytic converter flange mounting nuts from the muffler.
7. Remove the catalytic converter from the muffler.
8. Remove the exhaust manifold flange mounting nuts from the catalytic converter. Catalytic converter 4.3L engine
   
   
9. Remove the catalytic converter from the support bracket insulator.
10. Remove the catalytic converter and gaskets.
11. Remove the heated oxygen sensor.

To Install:

1. Install the heated oxygen sensors as needed.
2. Install a new gasket and the Install the catalytic converter to the support bracket insulator.
3. Install the catalytic converter to the exhaust manifold flange. Install the mounting nuts.
   • Tighten to 39 ft lbs (53 Nm).
4. Using a new flange gasket, install the catalytic converter to the muffler. Install the mounting nuts.
   • Tighten to 30 ft lbs (40 Nm).
5. Connect the left and right pre-converter heated oxygen sensor (HO2S) electrical connectors.
6. Connect the post-converter (HO2S) electrical connector.
7. Install the transmission support.
8. Lower the transmission.
9. Lower the vehicle.

---
It looks like you can cut them and replace them with new bolts and nuts.

their not on muffler their in front of and after the catalytic converter screwed into the exhaust pipe jack up and support vehicle and follow exhaust pipe from engine rear ward will see o2 sensor sticking upward with wires

there should be 2, one is either in the exhaust manifold or between the exh manifold and the converter,and the rear or downstream is after the converter.

They are located on your exhaust between your exhaust manifold and your catalytic converter. You should have two of them.

Look before and after the catalytic converters. They will have wiring connected to them.

It is most likely a bad front wheel speed sensor.Your sure abs rings were on back of rotors?It is going to be next to impossible to fix without getting the code with a scanner